In general X-ray imaging, an object is examined by taking absorption measurements of X-radiation penetrating the object of interest. While fine absorption differences within the object may be displayed with sufficient detail, areas within the object having a similar chemical composition, thereby having a similar absorption characteristics, may only be displayed with unsatisfactory detail.
Advancements in X-ray imaging technology provided phase-contrast imaging techniques taking into account the phase-shift of X-radiation passing through an object, which regularly is substantially stronger than a corresponding absorption. Interferometric measurement methods are employed to measure such a phase-shift of X-radiation within an object by irradiating the object with coherent X-radiation, while using a pair of gratings between the object and an X-ray detector to ultimately obtain phase information by using the grating pair to perform what is known in the art as phase stepping.
FIG. 1 shows a schematic representation of phase-contrast imaging. Source grating 12a is situated next to X-ray source 10 for generating spatially coherent X-radiation 48. Said X-Radiation 48 is penetrating object 14, subsequently passing through source grating 12b and analyzer grating 12c to ultimately arrive at X-ray detector 16. Source grating 12b and analyzer grating 12c are displaced relative to one another by a fraction of the grating periodicity to perform phase stepping. In each phase stepping state, x-ray image information may be acquired by X-ray detector 16, for obtaining an intensity-modulation with respect to the grating position for each single pixel.
Using phase-contrast imaging technology ultimately results in more than one image information type from one examination. In particular, at least four different types of images may be calculated from the acquired raw data, resulting in at least four different image information types.
Only one image type, the amplitude, attenuation or absorption image type, resembles known X-ray images from conventional technology. All other image types may have different properties and may thus look unfamiliar to an observer familiar with regular absorption X-ray images.
US 2010/0220834 A1 describes superposition of absorption images and phase-contrast images.